In manufacturing a semiconductor device, various processes such as etching, ashing, film formation and the like are performed on a semiconductor wafer as a target object. Such processes are carried out by using a plasma processing apparatus for performing a plasma process on a semiconductor wafer in a processing chamber that can be maintained at a vacuum atmosphere. In the plasma processing apparatus, an inner wall of the processing chamber is made of a metal such as aluminum or the like. Therefore, when a surface of the inner wall is exposed to a strong plasma, it is sputtered by bombardments of ions in the plasma to thereby generate particles. Accordingly, metal contamination is caused by the aluminum or the like, which has an adverse effect on device performance.
In order to solve the above-described problem, there has been suggested a technique for coating yttrium oxide on a portion exposed to a plasma in a processing chamber in an RLSA microwave plasma processing apparatus in which a plasma is generated by supplying microwave into the processing chamber by using a planar antenna (see, e.g., Japanese Patent Application Publication No. 2005-268763).
Meanwhile, along with the recent trend toward scaling up of a semiconductor wafer and miniaturization of devices, it is required to improve efficiency of the plasma process (e.g., film forming rate) and in-plane wafer surface processing uniformity. Hence, a method for performing a plasma process while applying a bias to a semiconductor wafer on a mounting table by supplying a high frequency power to an electrode which is embedded in the mounting table made of a dielectric material in a processing chamber of a plasma processing apparatus has been attracting attention in a film forming process represented by a plasma oxidation process.
When the high frequency power is supplied to the electrode of the mounting table, an opposite electrode needs to be provided in the processing chamber with a plasma processing space therebetween. The opposite electrode is preferably made of a conductive metal. In the plasma oxidation process, a plasma having strong oxidizing ability is generated near the opposite electrode, so that the surface of the opposite electrode is oxidized and degraded. In addition, the surface of the opposite electrode is sputtered, which results in metal contamination or particle generation.
Further, when the high frequency power is supplied to the electrode of the mounting table, a path of the high frequency current (RF return circuit) is formed, i.e., the high frequency current flows from the mounting table to the opposite electrode via the plasma processing space and then flows back from the opposite electrode to the earth of the high frequency power supply via the wall or the like of the processing chamber. If a stable high frequency current path is not formed, the plasma generated in the processing chamber becomes unstable. Furthermore, the power consumption efficiency of the high frequency power is decreased, so that the bias cannot be stably applied.
Moreover, if a short-circuit or an abnormal discharge occurs in the high frequency current path, the processing efficiency is decreased and the process becomes unstable. For example, if a short-circuit occurs on the high frequency current path such that the high frequency power flows toward the sidewall of the processing chamber which is relatively closely located instead of flowing toward the opposite electrode via the plasma processing space from the mounting table, the power consumption efficiency of the high frequency power is decreased and, also, the processing efficiency is decreased.